JP6176002B2 - Image forming apparatus and control method thereof - Google Patents

Description

The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that efficiently discharges deteriorated toner and extends the life of a development-related member , and a control method thereof .

  Conventionally, an electrophotographic image forming apparatus is known. In this image forming apparatus, generally, a photosensitive drum is uniformly charged and initialized, an electrostatic latent image is formed on the photosensitive drum by optical writing, and the electrostatic latent image is converted into a toner image. Is directly or indirectly transferred onto a transfer material such as paper and fixed by a fixing unit.

  The type in which the toner image is indirectly transferred to the paper is such that the toner image is primarily transferred from the image forming unit to an intermediate transfer belt or the like as an intermediate transfer member, and then secondarily transferred from the intermediate transfer belt to the paper. Many.

  In any case, in the electrophotographic image forming apparatus, a cleaning blade is installed to clean the untransferred toner on the photosensitive drum, and in the image forming apparatus having the transfer belt, the transfer belt is cleaned. A cleaning blade is installed.

  Generally, toner is a mere granular powder when viewed macroscopically, but is an irregularly shaped granule when viewed microscopically. Due to the irregular shape, the residual toner acts as a lubricant between the cleaning blade and the photosensitive drum or between the transfer belt and contributes to the improvement of the cleaning property.

  However, if the toner is used for a long time without replacing the old and new, the toner loses the irregularities and becomes nearly spherical. As the amount of toner with no irregularities increases, the function as a lubricant is diminished, and the coefficient of friction between the cleaning blade and the photosensitive drum increases, resulting in a noise called squealing or lacking in the cleaning blade. May occur. The cleaning property is also lowered.

  In addition, when the toner in the developing device is not used and is continuously rotated, an external additive such as alumina added to give fluidity to the toner is embedded in the toner and deteriorated. In some cases, transferability may deteriorate.

  In order to prevent these problems, the toner in the developer is discharged regularly or irregularly to reduce the proportion of the deteriorated toner and restore its function as a lubricant, so that functional toner is always maintained. Has been done. This toner discharge process is usually performed by turning on the write head and developing toner in that portion (reversal development process).

  With regard to the discharge of the deteriorated toner, for example, in an image forming apparatus having a developing device of a type in which two developing sleeves (developing rollers) are provided at the top and bottom of an opening of one developing device in order to increase the developing speed. There has been proposed a method for effectively discharging the toner from the lower sleeve by increasing the rotational speed of the lower sleeve. (For example, refer to Patent Document 1.)

  In the technique described in Patent Document 1, it is important to control the rotational speed of the upper sleeve so that the relative speed between the upper and lower sleeves is not higher than that during normal development when toner is discharged from the lower sleeve. .

JP 2009-122443 A

  However, the technique described in Patent Document 1 is specialized in a developing device of a multiple developing sleeve type in which two developing sleeves are provided at the top and bottom of an opening of one developing device in an effective discharging method of deteriorated toner. However, it is not a technique that can be directly applied to a developing device having one developing sleeve in one developing device that is still widely used today.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that efficiently discharges deteriorated toner and prolongs the life of a development-related member , and a control method thereof. .

In order to solve the above problems, an image forming apparatus according to the present invention includes a photosensitive member, a first cleaning blade for removing toner on the peripheral surface of the photosensitive member, a transfer belt, and a peripheral surface of the photosensitive member. A charging member that charges the circumferential surface of the photoconductor to a predetermined potential by applying the superimposed DC charging bias and AC charging bias, and the circumferential surface of the photoconductor that is charged to the predetermined potential is used for normal printing. The electrostatic latent image is developed as a toner image by an exposure member that is exposed based on image information to form an electrostatic latent image on the peripheral surface of the photoreceptor, and a DC developing bias and an AC developing bias applied in an overlapping manner. A developing member; and a transfer member that applies a DC transfer bias to the transfer belt to transfer the toner image from the photoreceptor to the transfer belt. The exposure member stops exposure, and the transfer member DC transfer bar The charging application is stopped, the charging member stops applying only the DC charging bias, and the charging member continues to apply the AC charging bias, and the DC developing bias and the AC developing bias are applied to the developing member. In a state where the application is continued, the photosensitive member is rotated, and the developing member discharges a toner image onto the effective peripheral surface of the photosensitive member, and the leading end of the toner image reaches the position of the transfer member and the trailing end Before the toner passes the position of the transfer member, a part of the toner image physically adheres to the transfer belt and a part of the toner image remains on the peripheral surface of the photosensitive member. At the time when the position reaches the position, the application of the DC development bias and the AC development bias applied to the development member is stopped, and at the time when the trailing edge of the toner image passes the position of the transfer member, the charging member is Mark on the circumference of the photoconductor And application of the AC charging bias, the rotation of the photosensitive body is stopped, it is characterized.
Further, the control method of the present invention includes a photosensitive member, a first cleaning blade for removing toner on the peripheral surface of the photosensitive member, a transfer belt, and a DC charging bias superimposed on the peripheral surface of the photosensitive member. An AC charging bias is applied to charge the peripheral surface of the photoconductor to a predetermined potential, and the peripheral surface of the photoconductor charged to the predetermined potential is exposed based on image information of normal printing. An exposure member that forms an electrostatic latent image on the peripheral surface of the photosensitive member; a developing member that develops the electrostatic latent image as a toner image by a DC development bias and an AC development bias applied in an overlapping manner; and the transfer belt A transfer member that applies a DC transfer bias to the transfer member to transfer the toner image from the photoreceptor to the transfer belt, wherein the exposure member stops exposure, and the transfer member D The application of the transfer bias is stopped, the charging member stops applying only the DC charging bias, and the charging member continues to apply the AC charging bias, and the DC developing bias and the AC developing bias applied to the developing member. The developing member discharges a toner image onto the effective peripheral surface of the photosensitive member, and the leading end of the toner image reaches the position of the transfer member. Before the end passes through the position of the transfer member, a part of the toner image physically adheres to the transfer belt and a part of the toner image remains on the peripheral surface of the photosensitive member. at time reaching the position of application of the DC developing bias and an AC developing bias applied to the developing member is stopped, at the time the rear end of the toner image has passed the position of the transfer member, said charging member Of the above photoreceptor And application of the AC charging bias applied to the surface, the rotation of the photosensitive body is stopped, it is characterized.

The present invention can provide an image forming apparatus that efficiently discharges deteriorated toner and extends the life of a development-related member , and a control method thereof.

1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (printer) according to Embodiment 1 of the invention. (a), (b) is an expanded sectional view which shows the developing device of the printer based on Example 1 with a photosensitive drum. FIG. 3 is a cross-sectional view illustrating an internal configuration and a developer reflux path by cutting the developing device of the printer according to the first embodiment in a direction indicated by an arrow g in FIG. (a) is a diagram showing the effective width of each of the charging roller, paper, optical writing head, developing roller, and cleaning blade from above, and (b) is a schematic enlarged view of these components. 1 is a circuit block diagram including a printer control device according to Embodiment 1. FIG. (a) shows from the top the rotation of the motor (not shown), the DC voltage of the primary transfer roller, the DC voltage and AC voltage of the charging roller, the lighting drive of the optical writing head, and the DC of the developing roller of the printer according to the first embodiment. (B) is a conventional printer shown for reference. From the top, rotation of a motor (not shown), DC voltage of a primary transfer roller, DC voltage and AC voltage of a charging roller, 5 is a driving timing chart of lighting driving of the optical writing head and DC voltage and AC voltage of the developing roller.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Example 1]

  FIG. 1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (hereinafter simply referred to as a printer) according to Embodiment 1 of the present invention.

  An image forming apparatus 1 shown in FIG. 1 is an electrophotographic secondary transfer tandem color image forming apparatus, and includes an image forming unit 2, a transfer belt unit 3, a toner supply unit 4, a paper feeding unit 5, and a belt. It is composed of a type fixing unit 6.

  The image forming unit 2 is in contact with the lower running unit surface 8a of the transfer belt 8 of the transfer belt unit 3 and multi-stages four developing devices 9 (9y, 9m, 9c, 9k) from right to left in FIG. Consists of a parallel configuration. The image forming unit 2 is held by a frame of the main body of the image forming apparatus 1 so that it can be moved up and down from the printing execution position shown in FIG. 1 to a maintenance position below it.

  Of the four developing devices 9, three developing devices 9y, 9m, and 9c on the downstream side (right side in the figure) are yellow (Y), magenta (M), and cyan (C), which are subtractive three primary colors, respectively. A mono-color image is formed with the color toner, and the developing device 9k forms a monochrome image mainly with black (K) toner used for characters and dark portions of the image.

  Each of the developing devices 9 has the same configuration except for the color of the toner that develops the image. Therefore, the configuration of the developing device 9k for black (K) toner will be described below as an example.

  The developing device 9 includes a photosensitive drum 10 at the top. The photosensitive drum 10 has a peripheral surface made of, for example, an organic photoconductive material. A cleaning blade 11, a charging roller 12, an optical writing head 13, and a developing roller 15 of the developing device 14 are arranged around the periphery of the photosensitive drum 10.

  The developing device 14 includes a first stirring / conveying member 16 and a second stirring / conveying member 17 in two developing tanks located below the developing roller 15. Details of the first and second stirring and conveying members 16 and 17 will be described later.

  The transfer belt unit 3 has an endless transfer belt 8 that extends in the shape of a flat loop in the left-right direction in the figure at approximately the center of the main unit, and the transfer belt 8 is stretched over the transfer belt 8. A driving roller 18 and a driven roller 19 are provided to circulate and move counterclockwise as indicated by arrows a and b in the figure.

  The above-described transfer belt 8 is directly transferred to the surface of the belt that circulates below by a primary transfer roller 21 that is integrated with the unit and pressed against the photosensitive drum 10 via the transfer belt 8 (primary transfer). Then, the toner image is conveyed to the secondary transfer unit 23 to the paper for further transfer (secondary transfer) to the paper.

  In the transfer belt unit 3, the cleaning blade 25 of the belt cleaner 24 is disposed in contact with the surface of the belt 18 that is stretched around the driving roller 18. A waste toner collecting container 26 is detachably disposed below the belt cleaner 24.

  In the belt cleaner 24, the cleaning blade 25 abuts on the surface of the transfer belt 8 to scrape and remove the waste toner, and the waste toner is sent to a lower waste toner collection container 26 by a conveying member.

  The toner supply unit 4 includes four toner hoppers 27 (27y, 27m, 27c, and 27k) disposed above the upper running unit of the transfer belt 8. The four toner hoppers 27y, 27m, 27c, and 27k contain yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively.

  The toner supply unit 4 includes yellow (Y), magenta (M), cyan (C), and black (Y) as indicated by Y, M, C, and K (hereinafter referred to as “YMCK”) in FIG. One of the toners K) is supplied to the developing device 14 of the developing device 9 through a toner supply path (not shown).

  The paper feed unit 5 includes one paper feed cassette 29. A large number of sheets 30 are stored in the sheet feeding cassette 29. A paper take-out roller 31, a feed roller 32, a separating roller 33, and a standby conveyance roller pair 34 are disposed in the vicinity of the paper feed port (right side of the drawing) of the paper feed cassette 29.

  In the paper conveyance direction (vertical upward direction in the figure) of the standby conveyance roller pair 34, a secondary transfer roller 35 that is in pressure contact with the driven roller 19 via the transfer belt 8 is disposed, and the secondary transfer roller 35 to the above-described paper 30 is provided. A transfer portion 23 is formed.

  A diffuse reflection type density sensor 36 is disposed in the vicinity of the lower running portion surface 8a of the transfer belt 8 at a substantially intermediate position between the secondary transfer portion 23 and the most downstream developing device 9y. A belt-type heat fixing unit 6 is disposed downstream (upward in the drawing) of the secondary transfer portion.

  Further downstream of the belt-type heat fixing unit 6, a pair of unillustrated unloading rollers for unloading the fixed sheet from the belt-type heat fixing unit 6 and a sheet discharge tray on which the unloaded paper is formed on the upper surface of the apparatus. A pair of paper discharge rollers (not shown) for discharging paper to 37 is disposed. An operation panel unit 38 is disposed at an upper end of the main body located to the right of the paper discharge tray 37 with a slight inclination.

  FIGS. 2A and 2B are enlarged sectional views showing the developing unit 14 together with the photosensitive drum 10. As shown in FIG. 2A, the developing device 14 includes two developing tanks 43 (43 a and 43 b) partitioned by an outer wall frame 41 and an inner partition wall 42.

  In the upper first developing tank 43a, the developing roller 15 and the first stirring / conveying member 16 described above are arranged. A doctor blade 44 is in contact with the developing roller 15. The second stirring / conveying member 17 described above is disposed in the lower second developing tank 43b. In the developing tank 43b, a toner density sensor 45 is arranged with its detection surface 46 exposed in the tank.

  The first stirring / conveying member 16 includes a rotating shaft 47 and a helical fin 48 fixed to the rotating shaft 47 in a spiral shape. The second stirring / conveying member 17 includes a rotation shaft 49 and a helical fin 51 fixed to the rotation shaft 49 in a spiral shape.

  If the toner density of the developer is less than the specified level, the toner density sensor 45 detects a decrease in toner density. When a decrease in toner density is detected, toner is supplied from a toner hopper 27 corresponding to the developing device 14 of the toner supply unit 4 through a supply port described later.

  Since the detection surface 46 of the toner density sensor 45 is exposed in the tank, the developer tends to stay on the detection surface 46. If the developer stays on the detection surface 46, the detection accuracy of the toner density sensor 45 is lowered.

  In order to prevent the detection accuracy of the toner density sensor 45 from being lowered, the rotation shaft 49 of the second agitating / conveying member 17 in the developing tank 43b is positioned so as to face the detection surface 46 of the toner density sensor 45. Further, a cleaning blade 54 comprising a blade holding portion 52 and an elastic sheet (blade) 53 held by the blade holding portion 52 is fixed.

  The cleaning blade 54 rotates together with the rotating shaft 49 of the stirring and conveying member 17, and rubs the detection surface 46 of the toner density sensor 45 with the elastic sheet 53 as shown in FIG. The developer to be retained is removed and replaced with the developer conveyed immediately thereafter. This prevents erroneous detection of the toner concentration that may be caused by the developer staying on the detection surface 46 of the toner concentration sensor 45.

  FIG. 3 is a cross-sectional view showing the internal structure and the developer reflux path by cutting the developing device 14 in the direction indicated by the arrow g in FIG. In FIG. 3, the same components as those shown in FIGS. 2A and 2B are denoted by the same reference numerals as those shown in FIGS. In FIG. 3, the cleaning blade 54 is not shown.

  As shown in FIG. 3, both end portions of the developing roller 15 are rotatably supported by the developing roller support portions 41 a and 41 b of the outer wall frame 41 of the developing device 14 via the rotation shaft 55. One end (left side in FIG. 3) of the rotation shaft 55 is formed to extend further than the developing roller support 41b, and is provided with a gear 56 at the tip.

  The outer wall frame 41 of the developing device 14 extends to the left in the same manner as the rotation shaft 55 of the developing roller 15 extends further than the developing roller support portion 41b to form an extended outer wall frame 41c. doing.

  A first circulation port 57 is formed inside the frame formed by the extended outer wall frame 41c. A toner supply port 58 is connected below the first circulation port 57 of the developing tank 43b.

  When a decrease in toner density is detected by the toner density sensor 45, toner is supplied from the toner hopper 27 of the toner supply unit 4 corresponding to the developing device 14 through the toner supply port 58.

  The rotary shaft 47 of the first agitating and conveying member 16 has one end rotatably supported by the outer wall frame 41 on the same side as the developing roller support portion 41a and the other end supported by the extended outer wall frame 41c. It is rotatably supported.

  A drive relay gear 59 is fixed to the outer end portion 47a that protrudes outside the extended outer wall frame 41c of the rotary shaft 47 of the first agitating and conveying member 16. In addition, an external engagement gear 61 and a drive transmission gear 62 are fixed to an external shaft 49 a that protrudes outside the extended outer wall frame 41 c of the rotation shaft 49 of the second agitating and conveying member 17.

  The drive transmission gear 62 rotates by engaging with a drive gear 65 of a developing device rotation device 66 composed of a motor 63 on the printer 1 main unit side, a rotation shaft 64 thereof, and a drive gear 65 fixed to the tip thereof. Then, the second agitation transport member 17 is rotated and the external engagement gear 61 is rotated.

  The external engagement gear 61 meshes with the drive relay gear 59 of the rotary shaft 47 of the first agitation transport member 16 and transmits the rotational drive to the drive relay gear 59. The drive relay gear 59 rotates the first agitation transport member 16 and relays the rotational drive from the external engagement gear 61 to the gear 56. The gear 56 rotates the developing roller 15.

  3 and 2 (a), the first stirring and conveying member 16 rotates counterclockwise in FIG. 2 (a) as indicated by an arrow c in FIG. While the developer is being stirred by the spiral fin 48, as shown by the arrow e in FIG. 2 (a), the developer is conveyed from the near side in the depth direction of the drawing to the other side (left side indicated by the arrows h, i, and j in FIG. 3). Then, the developer is supplied to the developing roller 15.

  The developing roller 15 supplies only the developer toner to the photosensitive drum 10 shown in FIGS. 1, 2A, and 2B, and converts the electrostatic latent image on the circumferential surface of the photosensitive drum 10 into a toner image. (develop. The developer carrier on the developing roller 15 from which only the toner is taken up by the photosensitive drum 10 is mixed with the developer in the developing tank 43a.

  The developer is sent back to the developing tank 43b from the first circulation port 57 on the other side (left side in FIG. 3) in the depth direction of FIG. 2A and 2B, as indicated by an arrow k.

  The second agitating / conveying member 17 in the developing tank 43b rotates counterclockwise as indicated by an arrow d in FIG. 2A, and the developer in the developing tank 43b is agitated by the spiral fins 51. Then, as indicated by the arrow f, the sheet is conveyed from the far side in the depth direction of FIG. 2A to the near side (the right side indicated by the arrows m, n, and o in FIG. 3).

  The second agitating / conveying member 17 stirs and conveys the developer from the second circulation port 67 on the near side in the depth direction in FIG. 3 (a) and 3 (b) (right side in FIG. 3) by the arrow p. As shown, the developer is sent to the developing tank 43a. In this way, the reflux of the developer and the replenishment of the toner are repeated, and the development with the toner proceeds sequentially.

  Although not shown in FIG. 1, the printer 1 of the present example has an electrical component disposed at the rear left part of the main unit, and a circuit in which a control device composed of a plurality of electronic components is mounted on the electrical component. The base is attached.

  FIG. 4A shows the effective charging width of the charging roller 12, the effective printing width of the paper 30, the effective head width of the optical writing head 13, the effective developing width of the developing roller 15, and the cleaning blade 11, 25 is a diagram showing the effective cleaning width of 25 in a correlative manner, and FIG. 4B is a diagram schematically showing an enlarged portion of the above configuration shown in FIG.

  A DC high voltage from a DC voltage power supply 78a and an AC high voltage from an AC voltage power supply 79a are superimposed and applied to the charging roller 12 from a high voltage unit 77 described later. Similarly, from the high voltage unit 77, the DC high voltage of the DC voltage power supply 78b and the AC high voltage of the AC voltage power supply 79b are superimposed and applied to the developing roller 15.

  In addition to the charging roller 12 and the developing roller 15 shown in FIG. 4A, although not shown in FIG. 4A, a DC high voltage is applied to the primary transfer roller 21 and the photosensitive drum 10 as well. Is done. As shown in FIG. 4A, there is a relationship of “optical writing head width <developing roller width <cleaning blade width” between the members.

  FIG. 5 is a circuit block diagram including the control device of the printer 1 having the above configuration. As shown in FIG. 5, the printer controller 70 is the center of the circuit block. An interface (I / F) 72 and a head controller unit 73 are connected to the printer controller unit 70 via a plurality of buses 71.

  The aforementioned operation panel unit 38 is connected to the I / F 72 via another bus 71. In addition, a signal such as print data is input to the I / F 72 from a host device (not shown) such as a personal computer.

  The I / F 72 transmits print data input from the outside to the head controller unit 73, and transmits command data included in the print data and instruction data input from the operation panel unit 38 to the printer controller unit 70.

  An EEPROM (electrically erasable programmable ROM) 74 and a ROM (read only memory) 75 are further connected to the printer controller 70 via a bus 71.

  The printer controller unit 70 reads out a control program stored in the ROM 75 and controls each unit according to the received sensor output in accordance with the read control program.

  The printer controller 70 receives sensor output signals from toner density sensors 45 (45y, 45m, 45c, 45k) for each developing unit 14 of yellow Y, magenta M, cyan C, and black K (hereinafter simply referred to as YMCK). Enter.

  The printer controller 70 monitors whether or not the sensor output signal of each toner density sensor 45 exceeds the toner supply threshold at the normal toner density control timing, and responds to each YMCK when the toner supply threshold is exceeded. The toner replenishing device 76 (76y, 76m, 76c, 76k) of the toner hopper 27 is driven to replenish toner to the developing device 9, and control is performed so as to keep the toner concentration of the two-component developer in the developing unit 14 constant. To do.

  Further, the printer controller unit 70 controls a driving motor of a roller rotation system (not shown) of the sheet feeding unit 5 on the other hand based on print data received from the outside via the I / F 72 to transfer the sheet to the secondary transfer unit. Transport to 23.

  On the other hand, based on the above print data, the printer controller unit 70 controls the photosensitive drum driving system for each YMCK to rotationally drive the photosensitive drum 10, and passes the light for each YMCK via the head controller unit 73. The process of forming an electrostatic latent image by optical writing on the photosensitive drum 10 by the writing head 13 (13y, 13m, 13c, 13k) is controlled.

  At this time, the printer controller unit 70 controls the high voltage unit 77 to apply bias voltages to the charging roller 12, the developing roller 15, and the primary transfer roller 21 of the developing device 9 (9k, 9c, 9m, 9y) for each YMCK. The driving power supplied to the optical writing head 13 is controlled separately at the timing of density control described later and when it is not the timing.

  Further, the printer controller unit 70 drives and rotates the developing device rotating device 66 (66y, 66m, 66c, 66k) for each YMCK to stir and convey the two-component developer in the developing device 14, and the developing device rotating device. The time or the number of rotations of the 66 motors 63 is recorded in a predetermined storage area of the EEPROM 74 for each YMCK.

  In this example, in the configuration shown in FIGS. 1 to 4, the optical writing head 13 is not issued and driven by the control by the control device shown in FIG. Processing for performing effective toner discharge will be described below.

  FIG. 6A shows the rotation of the motor (not shown) of this example, the DC voltage of the primary transfer roller 21, the DC voltage and the AC voltage of the charging roller 12, the lighting drive of the optical writing head 13, and the developing roller from the top. It is a drive timing chart of 15 DC voltage and AC voltage.

  FIG. 6B shows the rotation of a conventional motor (not shown), the DC voltage of the primary transfer roller 21, the DC voltage and charging voltage of the charging roller 12, and the voltage of the optical writing head 13 from the top. 6 is a drive timing chart of rolling drive, DC voltage of the developing roller 15 and AC voltage.

  First, the conventional control method shown in FIG. 6B will be described. Conventionally, toner is discharged after the end of printing operation. First, in FIG. 6B, first, after the printing end time t0, the DC voltage bias of the primary transfer roller 21 is turned off and the optical writing head 13 is turned on at time t1.

  As a result, a solid print electrostatic latent image is formed on the photosensitive drum 10. All lighting of the optical writing head 13 (all LEDs are turned on) is turned off at time t2, but the DC / AC superimposed developing bias is applied until the electrostatic latent image portion passes the developing roller 15 until time t4. After the development, the motor is stopped at time t5 when the solid development portion passes the primary transfer portion. The DC / AC superimposed voltage of the charging roller 12 is turned off after continuing until time t3 before time t4.

  As a result, a part of the toner discharged from the developing roller 15 is transferred to the transfer belt 8, and a part of the toner is left on the photosensitive drum 10 to supply toner as a lubricant to the cleaning blades 11 and 25. It is something to try.

  In FIG. 6B, the time X from the time t2 to the time t4 needs to be equal to or longer than the time during which the peripheral surface of the photosensitive drum 10 travels the distance from the optical writing head 13 to the developing roller 15. Furthermore, time Y from time t2 to time t5 is required to be at least time X. With such a process, the effect of the discharged toner can be expected.

  However, as described above, since it is necessary to turn on the optical writing head 13 completely for discharging the toner, there is a problem that the life of the optical writing head 13 is shortened. Further, as shown in FIG. 4A, since there is a relationship of “optical writing head width <developing roller width <cleaning blade width”, the toner is not developed even when the optical writing head 13 is fully turned on. Will occur.

  For this reason, a cleaning blade may be missing at a portion where there is no discharged toner (a portion where toner is not developed). This problem can be solved if the width of the optical writing head 13 is widened. However, in order to increase the width of the optical writing head 13, LED element chips are also installed in portions unnecessary for normal printing processing. A substantial increase in cost is inevitable.

  Therefore, the inventor not only changes the width of the optical writing head 13 widely but also does not even turn on the optical writing head 13 and efficiently discharges the deteriorated toner to clean the development-related members. A control method shown in the drive timing chart of FIG. 6 (a) was considered as a method of extending the lifetime of the optical writing heads without causing damage to the blades.

  As described above, FIG. 6A shows from the top the rotation of the motor (not shown), the DC voltage of the primary transfer roller 21, the DC voltage and the AC voltage of the charging roller 12, the lighting drive of the optical writing head 13, and the development. 4 is a driving timing chart of DC voltage and AC voltage of a roller 15.

  In FIG. 6 (a), at time T0, the normal printing lighting drive of the optical writing head 13 is turned off. At this time, an electrostatic latent image for normal printing exists on the photosensitive drum 10 shown in FIG. 4 between the optical writing head 13 and the developing roller 15, and between the developing roller 15 and the primary transfer roller 21. There is an untransferred toner image of normal printing.

  6A, at time T1, the portion where the lighting drive of the optical writing head 13 is turned off, that is, the end portion of the toner image for normal printing, moves to the position of the primary transfer roller 21. At this point, the transfer of the toner image for normal printing onto the transfer belt 8 is completed. Here, the DC voltage bias of the primary transfer roller 21 is turned off and the DC voltage bias of the charging roller 12 is turned off.

  However, the AC voltage bias of the charging roller 12 continues to be on. As a result, the residual voltage on the photosensitive drum 10 rapidly converges to 0V, and is maintained at substantially 0V while the AC voltage bias of the charging roller 12 continues. The toner is not discharged onto the photosensitive drum 10 until the portion of the photosensitive drum 10 where the electric potential is 0 V reaches the position of the developing roller 15.

  When the portion of the photosensitive drum 10 having a potential of 0 V comes to the position of the developing roller 15, the application of the DC voltage bias and the AC voltage bias of the developing roller 15 continues, so that the developing roller 15 has a potential of 0 V. Toner is discharged over the entire width of the peripheral surface of the photosensitive drum 10.

  In FIG. 6A, the toner discharge start position reaches the position of the primary transfer roller 21 at time T2. At this time, both the DC voltage bias and the AC voltage bias of the developing roller 15 are turned off, and the toner discharge is stopped.

  Since the transfer bias of the primary transfer roller 21 has already been turned off at time T2 when the toner discharge is stopped, the photoconductor during time B from time T2 to time T3 when the portion of discharged toner passes the primary transfer roller 21. Part of the toner discharged onto the drum 10 is transferred onto the transfer belt 8 due to physical adhesion, and the toner that has not transferred remains on the photosensitive drum 10.

  At time T3 when all of the discharged toner has passed the position of the primary transfer roller 21, the AC voltage bias of the charging roller 12 is turned off and the rotation of the motor is stopped. As a result, a part of the desired amount and width of discharged toner is formed on the transfer belt 8 and partly on the photosensitive drum 10.

  Since the discharged toner on the transfer belt 8 and the photosensitive drum 10 reaches the cleaning blades 11 and 25 when the next printing process starts, and acts as a lubricant, No defects such as chipping occur.

  As described above, the present invention does not intend to control the amount or width of the discharged toner by the lighting time of the optical writing head 13, but the developing roller is provided at a portion where the potential of the photosensitive drum 10 is set to approximately 0V. The amount of discharged toner is controlled by the voltage bias application time to the photosensitive drum 10, and a solid print state of discharged toner is created over the entire width of the photosensitive drum 10, so that the lighting time of the optical writing head 13 is shortened and the toner discharging width is widened. Can be formed.

Although several embodiments of the present invention have been described, the present invention is included in the invention described in the claims and the equivalents thereof. Hereinafter, the invention described in the scope of claims of the present application will be appended.
[Appendix 1]

A photoreceptor,
A first cleaning blade for removing toner on the peripheral surface of the photoreceptor;
A transfer belt;
A charging member that applies a DC charging bias and an AC charging bias superimposed on the peripheral surface of the photoconductor to charge the peripheral surface of the photoconductor to a predetermined potential;
An exposure member that forms an electrostatic latent image on the peripheral surface of the photosensitive member by exposing the peripheral surface of the photosensitive member charged to the predetermined potential based on image information of normal printing;
A developing member that develops the electrostatic latent image as a toner image by a DC developing bias and an AC developing bias applied in an overlapping manner;
A transfer member that applies a DC transfer bias to the transfer belt to transfer the toner image from the photoreceptor to the transfer belt;
With
The exposure member stops exposure, the transfer member stops applying the DC transfer bias, the charging member stops applying only the DC charging bias, and
The charging member continues to apply an AC charging bias, and the DC developing bias and the AC developing bias are continuously applied to the developing member;
In state,
The photosensitive member is rotated, and the developing member discharges a toner image onto an effective peripheral surface of the photosensitive member,
A part of the toner image physically adheres to the transfer belt and a part of the photosensitive member passes through the position of the transfer member until the trailing end of the toner image reaches the position of the transfer member. An image forming apparatus that controls stop of application of the DC developing bias and the AC developing bias and stop of rotation of the photosensitive member so as to remain on the peripheral surface.
[Appendix 2]

The time T0 when the exposure member stops exposure, the time T1 when the transfer member stops applying the DC transfer bias and the charging member stops applying only the DC charging bias, and the tip of the toner image When the time when the position of the transfer member is reached is time T2, and the time when the trailing edge of the toner image passes the position of the transfer member is time T3, a DC developing bias and an AC developing bias applied to the developing member. The application is stopped at time T2, and the application of the AC charging bias applied by the charging member to the peripheral surface of the photosensitive member and the rotation of the motor that drives the rotating members of all the constituent members are performed at time T3. Stop,
The image forming apparatus as set forth in appendix 1, wherein:
[Appendix 2]

A second cleaning blade that removes toner on the surface of the transfer belt, and the toner that adheres to the transfer belt is removed from the second cleaning blade when normal printing is resumed after the entire constituent members stop. The toner remaining on the peripheral surface of the photoconductor acts as a lubricant for the first cleaning blade,
3. The image forming apparatus according to appendix 1 or 2, wherein:

  The present invention can be used in an image forming apparatus that efficiently discharges deteriorated toner and extends the life of members around the developing device.

DESCRIPTION OF SYMBOLS 1 Full color image forming apparatus 2 Image forming part 3 Transfer belt unit 4 Toner supply part 5 Paper feeding part 6 Belt type fixing unit 8 Transfer belt 8a Lower running part surface 9 (9m, 9c, 9y, 9k) Developing device 10 Photosensitive drum DESCRIPTION OF SYMBOLS 11 Cleaning blade 12 Charging roller 13 Optical writing head 14 Developing device 15 Developing roller 16 1st stirring conveyance member 17 2nd stirring conveyance member 18 Drive roller 19 Follower roller 21 Primary transfer roller 23 Secondary transfer part 24 Belt cleaner 25 Cleaning blade 26 Waste toner collection container 27 (27m, 27c, 27y, 27k) Toner hopper 29 Paper feed cassette 30 Paper 31 Paper take-out roller 32 Feed roller 33 Rolling roller 34 Standby transport roller pair 35 Secondary transfer roller 36 Diffuse reflection type Density sensor 37 Output tray 38 Operation panel 41 Outer frame 41a, 41b Developing roller support 41c Extending outer wall frame 42 Internal partition wall 43 Developer tank 43a First developer tank 43b Second developer tank 44 Doctor blade 45 Toner density sensor 45y Y toner density sensor 45m M toner density sensor 45c C toner density sensor 45k K toner density sensor 46 Detection surface 47 Rotating shaft 47a Outer end 48 Spiral fin 49 Rotating shaft 51 Spiral fin 52 Blade holding portion 53 Elastic sheet (blade)
54 Cleaning blade 55 Rotating shaft 56 Gear 57 First circulation port 58 Toner supply port 59 Drive relay gear 61 External engagement gear 62 Drive transmission gear 63 Motor 64 Rotating shaft 65 Drive gear 66 (66y, 66m, 66c, 66k) Development Rotating device 67 Second circulation port 70 Printer controller 71 Bus 72 I / F (interface)
73 Head Controller 74 EEPROM (electrically erasable programmable ROM)
75 ROM (read only memory)
76 (76y, 76m, 76c, 76k) Toner supply device 77 High pressure unit

Claims (6)

A photoreceptor,
A first cleaning blade for removing toner on the peripheral surface of the photoreceptor;
A transfer belt;
A charging member that applies a DC charging bias and an AC charging bias superimposed on the peripheral surface of the photoconductor to charge the peripheral surface of the photoconductor to a predetermined potential;
An exposure member that forms an electrostatic latent image on the peripheral surface of the photosensitive member by exposing the peripheral surface of the photosensitive member charged to the predetermined potential based on image information of normal printing;
A developing member that develops the electrostatic latent image as a toner image by a DC developing bias and an AC developing bias applied in an overlapping manner;
A transfer member that applies a DC transfer bias to the transfer belt to transfer the toner image from the photoreceptor to the transfer belt;
With
The exposure member stops exposure, the transfer member stops applying the DC transfer bias, the charging member stops applying only the DC charging bias, and
The charging member continues to apply an AC charging bias, and the DC developing bias and the AC developing bias are continuously applied to the developing member;
In state,
The photosensitive member is rotated, and the developing member discharges a toner image onto an effective peripheral surface of the photosensitive member,
A part of the toner image physically adheres to the transfer belt and a part of the photosensitive member passes through the position of the transfer member until the trailing end of the toner image reaches the position of the transfer member. At the time when the leading edge of the toner image reaches the position of the transfer member to remain on the peripheral surface, the application of the DC developing bias and the AC developing bias applied to the developing member is stopped, and the trailing edge of the toner image At the time when the charging member passes the position of the transfer member, the application of the AC charging bias applied by the charging member to the peripheral surface of the photosensitive member and the rotation of the photosensitive member are stopped.
An image forming apparatus. The time T0 when the exposure member stops exposure, the time T1 when the transfer member stops applying the DC transfer bias and the charging member stops applying only the DC charging bias, and the tip of the toner image When the time when the position of the transfer member is reached is time T2, and the time when the trailing edge of the toner image passes the position of the transfer member is time T3, a DC developing bias and an AC developing bias applied to the developing member. The application is stopped at time T2, and the application of the AC charging bias applied by the charging member to the peripheral surface of the photosensitive member and the rotation of the motor that drives the rotating members of all the constituent members are stopped at the time T3. To
The image forming apparatus according to claim 1. A second cleaning blade for removing toner on the surface of the transfer belt is provided. When all the components stop and then normal printing is resumed, the toner adhering to the transfer belt is applied to the second cleaning blade. The toner that acts as a lubricant and remains on the peripheral surface of the photoreceptor acts as a lubricant for the first cleaning blade.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Applying a DC charging bias and an AC charging bias superimposed on the photosensitive member, a first cleaning blade for removing toner on the peripheral surface of the photosensitive member, a transfer belt, and the peripheral surface of the photosensitive member; A charging member that charges the peripheral surface of the photosensitive member to a predetermined potential, and the peripheral surface of the photosensitive member that is charged to the predetermined potential are exposed on the basis of image information of normal printing to electrostatically adhere to the peripheral surface of the photosensitive member. An exposure member for forming a latent image; a developing member for developing the electrostatic latent image as a toner image by a DC development bias and an AC development bias applied in a superimposed manner; and a DC transfer bias applied to the transfer belt to A transfer member that transfers a toner image from the photoconductor to the transfer belt, and a control method for an image forming apparatus,
The exposure member stops exposure, the transfer member stops applying the DC transfer bias, the charging member stops applying only the DC charging bias, and
The charging member continues to apply an AC charging bias, and the DC developing bias and the AC developing bias are continuously applied to the developing member;
In state,
The photosensitive member is rotated, and the developing member discharges a toner image onto an effective peripheral surface of the photosensitive member,
A part of the toner image physically adheres to the transfer belt and a part of the photosensitive member passes through the position of the transfer member until the trailing end of the toner image reaches the position of the transfer member. At the time when the leading edge of the toner image reaches the position of the transfer member to remain on the peripheral surface, the application of the DC developing bias and the AC developing bias applied to the developing member is stopped, and the trailing edge of the toner image At the time when the charging member passes the position of the transfer member, the application of the AC charging bias applied by the charging member to the peripheral surface of the photosensitive member and the rotation of the photosensitive member are stopped.
A control method characterized by that. The time T0 when the exposure member stops exposure, the time T1 when the transfer member stops applying the DC transfer bias and the charging member stops applying only the DC charging bias, and the tip of the toner image When the time when the position of the transfer member is reached is time T2, and the time when the trailing edge of the toner image passes the position of the transfer member is time T3, a DC developing bias and an AC developing bias applied to the developing member. The application is stopped at time T2, and the application of the AC charging bias applied by the charging member to the peripheral surface of the photosensitive member and the rotation of the motor that drives the rotating members of all the constituent members are stopped at the time T3. To
The control method according to claim 4. The image forming apparatus includes a second cleaning blade that removes toner on the surface of the transfer belt, and when the normal printing is resumed after all the constituent members are stopped, the toner attached to the transfer belt is Acting as a lubricant for the second cleaning blade, and the toner remaining on the peripheral surface of the photoconductor acts as a lubricant for the first cleaning blade;
6. The control method according to claim 4 or 5, wherein: